Zhong Lin Wang


Zhong Lin Wang is a Chinese-born American physicist, materials scientist and engineer specialized in nanotechnology and energy science. He received his PhD from Arizona State University in 1987. He is the Hightower Chair in Materials Science and Engineering and Regents' Professor at the Georgia Institute of Technology, USA.

Education

He came to the US for graduate school through CUSPEA program organized by Tsung-Dao Lee.

Career

Wang was employed a visiting Lecturer at Stony Brook University from 1987 to 1988. After working as a research fellow in the following year at Cavendish Laboratory in the University of Cambridge, Wang joined Oak Ridge National Laboratory and the National Institute of Standards and Technology as a research scientist from 1990-1994. He was hired by Georgia Institute of Technology as an associate professor in 1995; he was promoted to full Professor in 1999, Regents' professor in 2004, and the Hightower Chair in Materials Science and Engineering in 2010. Wang was the Director of the Georgia Tech’s Center for Nanostructure Characterization from 2000-2015. He is the Founding Director, Director, and Chief Scientist at Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences since 2012.

Research accomplishments

Summary of Wang's accomplishments

Wang has made original and seminal contributions to the synthesis, discovery, characterization, and fundamental understanding of the physical properties of zinc oxide nanobelts and nanowires. He was the first to recognize and exploit the potential of ZnO nanostructures for innovative applications in energy, sensors, electronics, and optoelectronic devices. His discoveries and breakthrough works in developing nanogenerators have established the principle and technological road map for harvesting mechanical energy from the environment and biological systems for powering mobile sensors. Such power and sensor technology can find applications in internet of things, human-machine interfaces, robotics, artificial intelligence, and blue energy. He found that the theoretical origin of nanogenerators is the Maxwell's displacement current. His research on triboelectric nanogenerators and self-powered nanosystems has inspired worldwide efforts in academia and industry for harvesting ambient energy for micro-nano-systems, which is now a distinct discipline in energy science for future sensor networks and internet of things.
Wang coined and pioneered the fields of piezotronics and piezo-phototronics by introducing piezoelectric potential gated charge transport process in fabricating strain-gated transistors for new electronics, optoelectronics, sensors, and energy sciences. The piezotronic effect and piezo-phototronic effect first discovered by Wang have important impact to electronics and photonics of the third generation semiconductors. The piezotronic transistors have applications in smart MEMS/NEMS, nanorobotics, human-electronics interface and sensors.
Wang's pioneer work on in-situ measurements of mechanical and electrical properties of a single nanotube/nanowire inside a transmission electron microscope opens a new field of nanomechanics for TEM, which was what led to his seminal work on oxide nanostructures and the inventions of various “nanogenerator” devices. His early work on inelastic scattering in electron diffraction and imaging establishes the theory of high-angle annular dark field imaging in scanning transmission electron microscopy.
Wang has authored and co-authored 6 scientific reference and textbooks and over 1500 peer reviewed journal articles, 45 review papers and book chapters, edited and co-edited 14 volumes of books on nanotechnology, and held over 60 US and foreign patents. His Google scholar citation can be found at . His google scholar citation is over 231,000 with an h-index of over 236. Wang is ranked No. 1 in Google Scholar public profiles in Nanotechnology & Nanoscience both in total citations and h-index impacts: http://www.webometrics.info/en/node/198; in Highly Cited Researchers according to their Google Scholar Citations public profiles, Wang is ranked No. 21 in all fields: http://webometrics.info/en/node/58. Dr. Wang is ranked No. 15 among 100,000 scientists worldwide across all fields: https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3000384. The ranking was made based on six citation metrics.

Wang's major scientific contributions

1. Science and technology of nanogenerators:
1.1 Invented piezoelectric nanogenerators and pioneered the field of self-powered systems. The first report on the piezoelectric nanogenerators was carried out by Prof. Wang in 2016. The electricity was generated by harvesting mechanical energy using ZnO nanowire arrays. He first introduced the areas of nano-energy and self-powered systems in 2006. These areas of study lead to the creation of nanomaterials and nanodevices. They are highly efficient energy harvesting from the ambient environment. Such devices have essential applications in sensor networks, mobile electronics, and the internet of things.
1.2 Invented triboelectric nanogenerators for harvesting distributed energy. Before the invention of triboelectric nanogenerators by Prof. Wang in 2011, the mechanical energy harvesting mainly relies on the electromagnetic generator first invented by Faraday in 1831. The EMG is most efficient for high-frequency mechanical motions, such as more than 10–60 Hz, because at a low frequency, the outputs of EMG are rather low. The high-quality and regulated energy at a high frequency plays important roles in constructing our today's energy system. However, the distributed energy becomes more and more important, because the era has marched into the internet of things and artificial intelligence. The TENGs have shown obvious advantages over the EMG in harvesting low-frequency mechanical energy from the environment. The energy conversion based on TENG relies on contact-electrification and electrostatic induction effects, and the efficiency can reach 50-85%. The maximum output power density obtained so far is up to 500 W/m2. The TENGs can harvest energy from many kinds of sources, and have important applications in self-powered systems for portable electronics, biomedicine, environmental monitoring, and even large-scale power. So Prof. Wang is referred to as the father of nanogenerators.
1.3 Developed hybrid cell. In practice, the sustainable operation of device usually cannot be realized by scavenging only one type of energy. Wang first proposed the idea of simultaneously harvesting two or more different types of energy by using one device. In 2009, Wang realized the idea in the experiments, where a hybrid cell was developed to harvest the mechanical and solar energy. Besides multiple types of energy, the hybrid cell also includes the case of using two different approaches to harvest the same type of energy.
1.4 Built the first pyroelectric nanogenerator. Thermalelectric effect is a physical effect that applies the temperature gradient along a thermalelectric material to generate electricity. And in a piezoelectric material, the time variation of temperature can also cause the polarization for power conversion, which is the pyroelectric effect. In 2012, based on the pyroelectric effect, the first pyroelectric nanogenerator was first built by Wang.
1.5 Coined the field of blue energy. The TENGs invented by Wang have been proved to be capable of harvesting water wave energy at a low frequency. However, using the traditional EMG technology, it is almost impossible in practice. In 2014, Wang proposed the idea of blue energy, in which using millions of TENG units to form a TENG network floating on water surface for large-scale wave energy harvesting. Such energy source has exhibited obvious advantages relative to other energy sources, because it has little dependence on weather and climate conditions. If one TENG unit can generate a power of 10 mW, the total power for the area equal to the size of Georgia state and 10 m depth of water is theoretically predicted to be 16 TW, which can meet the energy needs of the world. This initiative opens the new chapter for large-scale blue energy.
1.6 Established the theory of nanogenerators from the Maxwell's displacement current. In 1861, Maxwell proposed the main term ε??/?? of Maxwell's displacement current, leading to the emerging of electromagnetic wave in 1886. The electromagnetic wave sets the foundation of wireless communication, radar and later the information technology. Wang added the second term ???/?? into the Maxwell's displacement current for the cases when the surface polarization is present, which represents the polarization introduced by non-electric field related effects such as piezoelectric and triboelectric effects. The nanogenerators are the technology dominated by the Maxwell's displacement current, which lights the applications of Maxwell's displacement current in fields of energy and sensors. It is shown that the EMG is based on the time variation of magnetic field B, while the nanogenerator relies on the time variation of surface polarization field ??. Moreover, the nanogenerator has been demonstrated to have killer applications in harvesting low-frequency, irregular mechanical energy in our daily life.  
1.7 Unified the origins of contact-electrification. For decades, scientists have been debating about the charge identity and mechanisms of contact-electrification, if it is due to electron, ion and/or materials species transfer. Recently, Wang concluded that electron transfer is the dominant mechanism for CE between solid-solid pairs. Usually, when the interatomic distance between the two materials is shorter than the normal bonding length, which is in the region of repulsive forces, the electron transfer can occur. Recently, Wang proposed a generic model for the CE, and revealed that the electron transition between the atoms/molecules is induced by a strong electron cloud overlap between the two atoms/molecules in the repulsive region, because the interatomic potential barrier can be reduced. The contact/friction force can enhance the overlap of electron cloud. This model can be further extended to the cases of liquid-solid, liquid-liquid and even gas-liquid. Based on the generic model, a new process for forming an electric double layer between liquid and solid has been recently proposed by Wang.
1.8 Pioneered the ideas of energy for the new era and entropy for energy utilization. When we enter the new era of internet of things, sensor networks, big data, robotics and artificial intelligence, billions of small, mobile and distributed energy sources are greatly required. Realizing the "self-powering" is imperative, due to the major disadvantages of batteries. Wang proposed the idea of "energy for the new era" in 2017 to distinguish the distributed energy sources from the well-known new energy. Recently, Wang proposed the entropy theory of energy distribution and utilization for the era of internet of things. The "ordered" energy transmitted from power plants is used to solve the "ordered" applications for fixed sites and part of "disordered" distributed power applications, while the "disordered" energy harvested from the environment is mainly to solve distributed applications. This is a new field orientation for energy harvesting.
2. Piezotronics and piezo-phototronics of the third generation semiconductors
2.1 Discovered the piezotronic effect and coined the field of piezotronics. When applying a stress on a material with a non-centrosymmetric crystal structure, a piezoelectric potential ' can be produced due to the ion polarization. For a ZnO nanowire, the Schottky barrier height between the nanowire and its metal contact can be effectively tuned by the created internal field. So that the charge carrier transport process across the interface can be effectively tuned and gated. Such phenomenon is called as the piezotronic effect, which was first discovered by Prof. Wang in 2007. Wang has developed the piezoelectric field effect transistors, piezoelectric diodes and strain gated logic operations by applying the piezotronic effect. Then the field of piezotronics was coined, representing the electronics in which the piezopotential acts as a gate voltage. Based on the piezotronics, the design of traditional CMOS transistor can be essentially changed. First, the piezotronic transistor can have no gate electrode. Second, an internal piezopotential displaces the gate voltage applied, and the applied strain is used to control the device instead of the gate voltage. Third, the contact at the drain -nanowire interface controls the charge carrier transport instead of the channel width. Recently, the piezotronic effect in 2D materials was also first demonstrated by Wang. The piezotronics will find important and wide applications in human-computer interfacing, smart MEMS, nanorobotics and sensors in future.
2.2 Discovered the piezo-phototronic effect and coined the field of piezo-phototronics. When applying a stress, the piezopotential created by interface polarization charges can greatly tune the local band structure and shift the charge depletion zone at a pn junction. The separation or recombination of charge carriers at the junction can be effectively enhanced as excited by photon. Such phenomenon is called as the piezo-phototronic effect, first discovered by Wang in 2009, in which the optoelectronic processes are tuned and controlled by the created piezopotential. By using this effect, Wang has reported pressure/force sensor arrays based on individual-nanowire LED, which can map strain at a high resolution and density and greatly enhance the efficiency of LED. Such effect as a new physics effect will find important applications in improving the performance of optoelectronic devices.
2.3 Discovered the piezophotonic effect
Wang first theoretically predicted the piezoelectric-induced photon-emission effect in 2008. The photo emission can occur, resulting from the drop of trapped charges from the vacancy/surface states back to the valence band, under the existence of the piezoelectric potential. Such effect has been experimentally observed and verified in his later work.
2.4 Initiated tribotronics
Similar to using a piezoelectric potential to control the carrier transport in a semiconductor device, the triboelectric potential can also be used as the gate voltage of a FET device. This is a new approach to transform the biomechanical motion into an electronic control, resulting in the emerging of a new field called as tribotronics. So far, different kinds of tribotronic functional devices, such as tribotronic tactile switch, memory, hydrogen sensor and phototransistor, have been fabricated.
3. Growth and understanding ZnO nanostructures.
Nanobelts are a new kind of 1D nanostructure formed by various semiconducting oxides having different cations and crystallographic structures. The first paper on the oxide nanobelts published in Science is one of the top 10 most cited papers in materials science in last decade. It has laid the foundation for other subsequent researches. The ZnO has become a kind of material which has the equal importance to Si nanowires and carbon nanotubes. Wang has been leading the ZnO nanostructure study in the world since 2000.
4. In-situ nanomeasurements in TEM.
The characterizations of physical properties for carbon nanotubes, which are influenced by the sample purity and nanotube size distribution, are usually carried on by scanning probe microscopy. In 1999, a series of unique techniques were developed by Wang and co-workers based on the transmission electron microscopy to measure the properties of individual nanotubes, including the mechanical, electrical and field emission ones. By using the in-situ TEM technique, one can directly observe the crystal and surface structures of the material at atomic-resolution, and also carry out nanoscale property measurements. Wang demonstrated a nanobalance technique and a novel approach toward nanomechanics, regarded as the breakthrough in nanotechnology in 1999 by APS. A new field of in-situ nanomeasurements in materials science and mechanics was opened.
5. Theory of inelastic scattering in electron diffraction and imaging.'
Original contributions have been made by Wang to understand the inelastic scattering in electron diffraction and imaging. His textbook on Elastic and Inelastic Scattering in Electron Diffraction and Imaging'' is regarded as "a noteworthy achievement and a valuable contribution to the literature". In scanning transmission electron microscopy, the high-angle annular dark-field is dominated by the thermal diffuse scattering, which is revealed by Wang. And the dynamic theory for including TDS in image simulation of HAADF was first proposed by Wang.

Awards and honors

Wang has received numerous honors and awards. They include: Albert Einstein World Award of Science, conferred by the World Cultural Council ; ; ; American Chemical Soc. Publication most prolific author ; Global Nanoenergy Prize, The NANOSMAT Society, UK ; Distinguished Research Award, Pan Wen Yuan foundation ; Outstanding Achievement in Research Innovation award, Georgia Tech ; Distinguished Scientist Award from Southeastern Universities Research Association ; Thomson-Reuters Citation Laureate in Physics ; Distinguished Professor Award ; NANOSMAT prize ; China International Science and Technology Collaboration Award ; World Technology Award ; The James C. McGroddy Prize for New Materials from American Physical Society ; ACS Nano Lectureship ; Edward Orton Memorial Lecture Award, American Ceramic Society ; MRS Medal from Materials Research Society ; Purdy award, American Ceramic Society ; John M. Cowley Distinguished Lecture, Arizona State University ; NanoTech Briefs, Top50 award ; Sigma Xi sustain research awards, Georgia Tech ; Georgia Tech faculty outstanding research author award ; S.T. Li Prize for Distinguished Achievement in Science and Technology ; Outstanding Research Author Award, Georgia Tech ; Burton Medal, Microscopy Society of America.
Wang was elected as a foreign member of the Chinese Academy of Sciences in 2009, member of European Academy of Sciences in 2002, academician of Academia of Sinica 2018, International fellow of Canadian Academy of Engineering 2019; fellow of American Physical Society in 2005, fellow of AAAS in 2006, fellow of Materials Research Society in 2008, fellow of Microscopy Society of America in 2010, fellow of the World Innovation Foundation in 2002, fellow of World Technology Network in 2014, and fellow of Royal Society of Chemistry. Wang's breakthrough researches in the last 15 years has been broadly covered by over 50 media such as CNN, Reuters, Georgia Tech News, and youtube video lectures. Wang is the founding editor and chief editor of an international journal Nano Energy with an impact factor of 15.548. Citations of his research and h-index can be found at. Wang is a member of the Advisory Board of the newly launched .